CA Foundation · Paper 4 · Business Economics
Price-Output Determination under Different Market Forms
Unit 3 · Short Revision Sheet for May 2026 onwards
MCQ Priority
Short Notes
Quick Revision
Crux First
Most important recall points
- Perfect competition → firm is price taker.
- Perfect competition → AR = MR = Price.
- Firm equilibrium → MR = MC and MC must cut MR from below.
- Same market price can exist with different firm outputs.
- Short-run supply curve of competitive firm = MC above AVC.
- Shutdown rule → Price < AVC.
- Long-run perfect competition → only normal profit.
- Monopoly → single seller, price maker, AR downward, MR below AR.
- Monopoly fixes output first, then takes price from AR curve.
- Price discrimination → same product sold in different sub-markets at different prices.
- Discriminating monopoly equilibrium → MRA = MRB = MC.
- Monopolistic competition → differentiated product, many sellers, long run normal profit + excess capacity.
1. Perfect Competition
Main Features
- Large number of buyers and sellers
- Homogeneous product
- Free entry and exit
- Perfect knowledge
- Firm is a price taker
Perfect Competition: AR = MR = Price
2. Industry Price and Firm Output
- Industry determines market price through total demand and total supply.
- Each firm accepts that market price.
- But all firms need not sell the same quantity.
- At the same market price, one firm may sell 8 units, another 10, another 12 units.
Same market price does not mean same output for every firm.
3. Competitive Firm Equilibrium
- Firm is in equilibrium where profit is maximum.
- Main condition: MR = MC.
- Second condition: MC must cut MR from below.
Since MR = Price, competitive firm chooses output where Price = MC
MCQ Trap
- Firm chooses output, not price.
- Price is already fixed by the market.
4. Short Run Supply and Shutdown
- Competitive firm’s short-run supply curve is the MC curve above AVC.
- If price covers AVC, firm continues.
- If price falls below AVC, firm shuts down.
Short-run Supply Curve = MC above AVC
Shutdown Rule: Price < AVC
5. Competitive Firm: Profit Situations
| Condition |
Result |
| AR > ATC |
Supernormal profit |
| AR = ATC |
Normal profit |
| AVC < AR < ATC |
Loss, but continue |
| AR < AVC |
Shutdown |
6. Long Run Perfect Competition
- Free entry removes supernormal profit.
- Free exit removes losses.
- In the long run, only normal profit remains.
Long Run: LMC = LAC = P = MR
Long-run perfect competition gives optimum plant use and minimum possible cost.
7. Monopoly
Main Features
- Single seller
- No close substitute
- Strong barriers to entry
- Firm is a price maker
In monopoly, firm and industry are the same.
8. Monopoly Revenue and Equilibrium
- AR curve slopes downward.
- MR curve also slopes downward.
- MR lies below AR.
- Monopolist chooses output where MR = MC.
- After fixing output, price is taken from the AR curve.
Monopoly Equilibrium: MR = MC
Price is read from AR at equilibrium output
MCQ Trap
- Monopolist does not choose price first and then output.
- It chooses output first, then corresponding price.
9. Monopoly: Short Run and Long Run
- In short run, monopoly may earn supernormal profit or suffer loss.
- In long run, monopoly can continue to earn supernormal profit because entry is blocked.
- Long-run monopoly need not produce at minimum LAC.
10. Price Discrimination
- Same product sold at different prices in different markets.
- Possible only when seller has control over price.
- Market must be separable.
- Elasticity of demand should differ across markets.
- Resale between markets should not be possible.
Higher price is charged where demand is more inelastic.
11. Two Sub-Markets under Price Discrimination
- Monopolist may divide total market into sub-market A and sub-market B.
- Total output is first fixed.
- Then output is distributed between the two markets.
- Different prices may be charged in the two markets.
Equilibrium: MRA = MRB = MC
Total Output: OM = OM1 + OM2
This is the exact “same product, two markets, different prices” logic.
12. Monopolistic Competition
- Many sellers and many buyers
- Differentiated product
- Free entry and exit
- Some degree of price control
- Demand curve slopes downward
Equilibrium: MR = MC
13. Monopolistic Competition: Short Run and Long Run
- In short run, firm may earn profit or incur loss.
- In long run, entry and exit reduce everything to normal profit.
- But firm does not produce at optimum capacity.
Long Run: Normal Profit + Excess Capacity
14. Quick Comparison
| Feature |
Perfect Competition |
Monopoly |
Monopolistic Competition |
| Sellers |
Many |
One |
Many |
| Product |
Homogeneous |
No close substitute |
Differentiated |
| Price Control |
None |
High |
Some |
| Demand Curve |
Horizontal |
Downward sloping |
Downward sloping |
| Long-run Profit |
Normal only |
Can continue supernormal |
Normal only |
Final Quick Revision
1-minute recall before MCQs
- Perfect competition → price taker.
- Perfect competition → AR = MR = Price.
- Competitive equilibrium → MR = MC.
- Same price can exist with different outputs by different firms.
- Short-run supply curve = MC above AVC.
- Shutdown → Price < AVC.
- Long-run perfect competition → only normal profit.
- Monopoly → price maker, MR below AR.
- Monopoly chooses output first, then price from AR.
- Price discrimination → two markets, different prices.
- Discriminating monopoly equilibrium → MRA = MRB = MC.
- Monopolistic competition → differentiated product.
- Long-run monopolistic competition → normal profit + excess capacity.
